Object detector and sensor

ABSTRACT

An object detector includes a projector including a light source having a two-dimensionally arranged plurality of light emitter groups, each of the light emitter groups having a plurality of light emitters, a light receiver which receives light emitted from the projector, and reflected by an object, and a light source driver which lights on and lights off each of the light emitter groups of the light source.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.15,371,650, filed Dec. 7, 2016, which is a continuation of U.S.application Ser. No. 14/554,498 (now U.S. Pat. No. 9,568,605), filedNov. 26, 2014, which is based on and claims priority from JapanesePatent Application No. 2013-252683, filed on Dec. 6, 2013, and JapanesePatent Application No. 2014-002813, filed on Jan. 10, 2014, thedisclosures of each of which are hereby incorporated by reference intheir entirety.

BACKGROUND Field of the Invention

The present invention relates to an object detector and a sensor, inparticular, to an object detector using an object as a detection targetand a sensor including the object detector.

Description of the Related Art

The development of a sensor using laser light has increased considerablyin recent years.

For example, JP 3446466B discloses a reflection sensor including arotating polygon mirror, a pulse light incident unit which emits pulselight to enter into the rotating polygon mirror from a predetermineddirection, and a light receiver which receives the pulse light emittedfrom a reflection surface of the rotating polygon mirror to a forwardmeasurement area, and reflected by an object in the measurement area.

As another example, JP 2894055B discloses a laser radar which isinstalled in a vehicle, and determines the existence or non-existence ofan obstacle from object-reflected light of laser light emitted in aforward space in a traveling direction.

However, in the devices disclosed in JP 3446466B and JP 2894055B, it isdifficult to satisfy an increase in distance to a detectable object,expansion of a detection region in an up and down direction, andimprovement in detection resolution performance in an up and downdirection.

SUMMARY

One embodiment of the present invention provides an object detector,including: a projector including a light source having atwo-dimensionally arranged plurality of light emitter groups, each ofthe light emitter group having a plurality of light emitters; a lightreceiver which receives light emitted from the projector, and reflectedby an object; and a light source driver which lights on and lights offeach of the light emitter groups of the light source.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide further understandingof the invention, and are incorporated in and constitute a part of thisspecification. The drawings illustrate an embodiment of the inventionand, together with the specification, serve to explain the principle ofthe invention.

FIG. 1 is an external view illustrating a vehicle in which a laser radar20 according to one embodiment of the present invention is installed.

FIG. 2 is a block diagram illustrating a configuration of a monitor 10according to one embodiment of the present invention.

FIG. 3 is a view illustrating the configuration of the laser radar 20.

FIG. 4 is a view illustrating a plurality of light emitter groups in alight source 21.

FIG. 5 is a view illustrating one light emitter group.

FIG. 6 is a view illustrating light emitter groups G (i, j).

FIG. 7 is a view illustrating a light source driver.

FIG. 8 is a view illustrating a relationship between a select signal anda light emitter group selected by a selector.

FIG. 9 is a view illustrating a light-receiving timing detection unit.

FIG. 10 is a view illustrating a light-receiving timing signal.

FIG. 11 is a flowchart illustrating a performance of an objectinformation-obtaining unit.

FIG. 12 is a timing chart illustrating a lighting-on time of one lightemitter group.

FIG. 13 is a timing chart illustrating a relationship between drivingcurrent and a selected light emitter group.

FIGS. 14A, 14B are views each illustrating a divergence angle.

FIG. 15 is a view illustrating a relationship between a divergent angleand a focal length f of a coupling lens 23.

FIGS. 16A, 16B are views each illustrating a detection region.

FIGS. 17A, 17B are views each illustrating a detection angle.

FIG. 18 is a view illustrating a relationship between a detection angleand a focal length f of the coupling lens 23.

FIGS. 19A, 19B are views each illustrating a reflected light-receivingarea of a light receiver 25.

FIGS. 20A, 20B are views each illustrating a mask M provided in thelight receiver 25.

FIG. 21 is a block diagram illustrating a configuration of a sound andalarm generator.

FIGS. 22A, 22B are views each illustrating the size of thelight-receiving area of the light receiver 25 when a focal length of alight-receiving lens 24 is increased in the Z-axis direction.

FIGS. 23A, 23B are views each illustrating the size of thelight-receiving area of the light receiver 25 when a focal length of thelight-receiving lens 24 is decreased in the Y-axis direction.

FIG. 24 is a view (part 1) illustrating an example including twocoupling lenses (23_1, 23_2) each having a different focal lengthinstead of the coupling lens 23, and two light-receiving lenses (24_1,24_2) each having a different focal length instead of thelight-receiving lens 24.

FIG. 25 is a view (part 2) illustrating an example including twocoupling lenses (23_1, 23_2) each having a different focal lengthinstead of the coupling lens 23, and two light-receiving lenses (24_1,24_2) each having a different focal length instead of thelight-receiving lens 24.

FIG. 26A is a view illustrating light toward a peripheral part of thedetection region.

FIG. 26B is a view illustrating light toward a central part of thedetection region.

FIG. 27A is a view illustrating light from the peripheral part of thedetection region.

FIG. 27B is a view illustrating light from the central part of thedetection region.

FIG. 28 is a view illustrating a difference between an object located inthe central part of the detection region and an object located in theperipheral part of the detection region.

FIG. 29 is a view illustrating assembly light emitter groups.

FIG. 30 is a flowchart illustrating a modified example of a performanceof an object information-obtaining unit.

FIG. 31 is a flowchart illustrating details of Step S505 in FIG. 30.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, one embodiment of the present invention will be describedwith reference to FIGS. 1 to 21. FIG. 1 illustrates the externalappearance of a vehicle 1 in which a laser radar 20 as an objectdetector according to one embodiment of the present invention isinstalled.

The laser radar 20 is attached near the front number plate of thevehicle 1 as one example. In addition, in this embodiment, a directionorthogonal to a road surface is the Z-axis direction, and a forwardmovement direction of the vehicle 1 is the +X direction in XYZthree-dimensional orthogonal coordinates.

As illustrated in FIG. 2 as one example, the vehicle 1 includes insidethereof a display 30, main controller 40, memory 50, and sound and alarmgenerator 60. These are electrically connected through a datatransmittable bus 70.

A monitor 10 as a sensor includes the laser radar 20, display 30, maincontroller 40, memory 50, and sound and alarm generator 60.

The laser radar 20 includes, as illustrated in FIG. 3 as one example, alight source 21, light source driver 22, coupling lens 23,light-receiving lens 24, light receiver 25, light-receiving timingdetection unit 26, and object information-obtaining unit 27.

The light source 21 includes a plurality of light emitters. Each lightemitter is Vertical-Cavity Surface-Emitting Laser (VCSEL). Namely, thelight source 21 includes a VCSEL array.

As illustrated in FIG. 4 as one example, a plurality of light emittersof the light source 21 is divided into a plurality of light emittergroups G arranged in a matrix. In each light emitter group G, asillustrated in FIG. 5 as one example, a plurality of light emitters istwo-dimensionally arranged.

In this case, as one example, each light emitter group G includes 12560(=157×80) light emitters two-dimensionally arranged at equal intervalssuch that 157 light emitters are arranged in the Y-axis direction and 80light emitters are arranged in the X-axis direction. When the lightoutput of one light emitter is 2 mW, and 12560 light emitters aresimultaneously lighted on, the light output of one light emitter group Gis about 25 W.

When a diameter ds of one light emitter is 1 μm, a distance D1 betweentwo light emitters adjacent to each other in the Y-axis direction is 1μm and a distance D2 between two light emitters adjacent to each otherin the Z-axis direction is 1 μm, and a length L1 of one light emittergroup G in the Y-axis direction is 313 μm and a length L2 of one lightemitter group G in the Z-axis direction is 159 μm.

As one example, the light source 21 includes 192 (=16×12) light emittergroups G arranged in matrix at equal intervals such that 16 lightemitter groups G are arranged in the Y-axis direction and 12 lightemitter groups G are arranged in the Z-axis direction. In addition, whenit is necessary to distinguish 192 light emitter groups G, asillustrated in FIG. 6, the light emitter groups are represented as G (i,j) with the arrangement sequence in the −Z-axis direction as i (1≤i≤12)and the arrangement sequence in the +Y-axis direction as j (1≤j≤16).

A length L3 of the light source 21 in the Y-axis direction is 5.008 mm(=313 μm×16), and a length L4 of the light source 21 in the X-axisdirection is 1.908 mm (=159 μm×12).

A distance D3 between the two light emitter groups adjacent to eachother in the Y-axis direction is set such that a space between the lightemitter located on the most +Y side in the light emitter group on the −Yside and the light emitter located on the most −Y side in the lightemitter group on the +Y side is equal to D1.

A distance D4 between the two light emitter groups adjacent to eachother in the Z-axis direction is also set such that a space between thelight emitter located on the most +Z side in the light emitter group onthe −Z side and the light emitter located on the most −Z side in thelight emitter group on the +Z side is equal to D2.

Namely, a plurality of light emitters in the light source 21 is arrangedat equal intervals in the Y-axis direction and the Z-axis direction.With this arrangement, an even resolution performance can be achieved,and the processes in the object information-obtaining unit 27 can besimplified.

In this case, the light emitter groups having i=1 to 8 are for a frontsurface, and the light emitter groups having i=9 to 12 are for a roadsurface.

Referring to FIG. 3, the light source driver 22 controls the driving ofthe light source 21 based on the instruction of the objectinformation-obtaining unit 27.

In this case, the light source driver 22 includes a selector whichinputs a light source driving signal and selects signals made of 8signals (I1 to I4, J1 to J4), as illustrated in FIG. 7 as one example.In this selector, as illustrated in FIG. 8, when I1=L (low level), I2=L,I3=L, I4=L, J1=L, J2=L, J3=L, and J4=L, for example, G (1, 1) isselected, and the light source driving signal is output to G (1, 1).Moreover, when I1=H (high level), I2=H, I3=L, I4=H, J1=H, J2=H, J3=H,and J4=H, for example, G (12, 16) is selected, and the light sourcedriving signal is output to G (12, 16).

The coupling lens 23 changes the light emitted from the light source 21into substantially parallel light. The light through the coupling lens23 is light to be emitted from the laser radar 20.

The light-receiving lens 24 is disposed on the optical axis of the lightemitted from the laser radar 20, and reflected by the object, so as tocollect the light.

The light receiver 25 receives the light collected by thelight-receiving lens 24, and outputs electric signals corresponding tothe received light volume.

The light-receiving timing detection unit 26 monitors an output signalof the light receiver 25, and detects the light-receiving timing of thelight reflected by the object.

In this case, as illustrated in FIG. 9 as one example, thelight-receiving timing detection unit 26 includes a current-voltageconvertor and a comparator. The current-voltage convertor converts thecurrent signal output from the light receiver 25 into the voltagesignal. The comparator outputs a light-receiving timing signal whichreaches a low level when the voltage of the voltage signal output fromthe current-voltage convertor is equal to the previously set voltage Vsor below, and reaches a high level when the voltage is larger than thevoltage Vs. As illustrated in FIG. 10 as one example, in thelight-receiving timing, the light-receiving timing signal is changedfrom the low level to the high level. The light-receiving timing signalis output to the object information-obtaining unit 27.

The object information-obtaining unit 27 instructs the light emittergroup to be lighted on and the lighting-on/lighting-off timing of thelight emitter group to the light source driver 22. The objectinformation-obtaining unit 27 obtains object information such as theexistence or non-existence of an object, distance to an object, size,shape, and position of an object based on the lighting-on timing and thelight-receiving timing signal from the light-receiving timing detectionunit 26.

FIG. 11 illustrates a flowchart of an object information-obtainingprocess which is executed by the object information-obtaining unit 27.In addition, the object information-obtaining unit 27 repeatedlyexecutes the object information-obtaining process at a predeterminedtiming (in this case, once in 20 seconds) until the power source isswitched off. The object information-obtaining unit 27 includes aninterruption controller having a timer function, and is informed byinterruption upon the elapse of a predetermined time (in this case,T1+T2, T0 (refer to FIG. 12)).

In the first Step S401, the variable numbers i, j which specify thelight emitter group are set to the initial value 1.

In the next Step S403, the select signal for selecting the light emittergroup G (i, j) is output to the light source driver 22.

In the next Step S405, the lighting-on of the selected light emittergroup G (i, j) is instructed to the light source driver 22. The lightsource driver 22 thereby simultaneously lights on all of the lightemitters in the light emitter group G (i, j) only for a predeterminedtime T1 (refer to FIG. 12). In this case, T1=0.02 μsec, as one example.

In the next Step S407, the timer counter TC in the interruptioncontroller is reset to 0. In addition, the value of the timer counter TCis counted up by the interruption controller.

In the next Step S409, it is determined whether or not the lightreflected by the object is received by the light receiver 25 based onthe light-receiving timing signal from the light-receiving timingdetection unit 26. When the light receiver 25 does not receive the light(NO in S409), the process moves to Step S411.

In Step S411, it is determined whether or not the value of the timercounter TC is equal to a value corresponding to T1+T2 (refer to FIG. 12)or more. In this case, as one example, T2 is 1.3 μsec which is a timerequired for returning the light reflected and scattered by the object200 m away. When there is no interruption at the time that the value ofthe timer counter TC reaches a value corresponding to T1+T2 from theinterruption controller (NO in S411), the process goes back to StepS409.

In addition, in Step S409, when the light receiver 25 receives light(YES in S409), the process moves to Step S413.

In Step S413, the existence of the object is determined.

In the next Step S415, the distance to the object is obtained based onthe value of the timer counter TC and the light-receiving timing of thelight receiver 25. Then, the obtained distance to the object is storedin a not-shown memory of the object information-obtaining unit 27together with the object existence information, the detection time, andthe values of valuable numbers i, j. Then, the process moves to StepS419.

In Step S411, when there is the interruption at the time that the valueof the timer counter TC reaches the value corresponding to T1+T2 fromthe interruption controller (YES in S411), the process moves to StepS417.

In Step S417, the non-existence of the object is determined. Thenon-existence object information is stored in a not-shown memory of theobject information-obtaining unit 27 together with the detection timeand the values of the valuable numbers i, j.

In the next Step S419, it is determined whether or not the value of thetimer counter TC is equal to a value corresponding to the time T0 (referto FIG. 12) or more. In this case, T0 is 104 μsec since the objectinformation-obtaining process is repeatedly executed once in 20 msec. Inthis case, the light source 21 is lighted on only for 0.02 μsec once in104 μsec. Thus, eyes can be protected. When there is no interruption atthe time that the value of the timer counter TC reaches the valuecorresponding to T0 from the interruption controller (NO in S419), theprocess waits for the interruption. When there is the interruption (YESin S419), the process moves to Step S421.

In Step S421, it is determined whether or not the value of the valuablenumber j is equal to 16 or more. When the value of the valuable number jis less than 16 (NO in S421), the process moves to Step S423.

In Step S423, 1 is added to the value number j, and the process returnsto Step S403.

The processes in Steps S403 to S423 are repeated until the value of thevaluable number j reaches equal to 16 or more (YES in S421).

When the value of the valuable number j reaches equal to 16 or more (YESin S421), the process moves to step S425.

In step S425, it is determined whether or not the value of the valuablenumber i is equal to 12 or more. When the value of the valuable number iis less than 12 (NO in S425), the process moves to Step S427.

In Step S427, 1 is added to the value of the valuable number i.

In the next Step S429, the value of the valuable number j is returned tothe initial value 1, and the process returns to Step S403.

The processes of Steps S403 to S429 are repeated (refer to FIG. 13)until the value of the valuable number i reaches equal to 12 or more(YES in S425).

When the value of the valuable number i reaches equal to 12 or more (YESin S425), the process moves to Step 5431.

In step S431, the information regarding the existence or thenon-existence of the object and the distance to the object are read froma not-shown memory of the object information-obtaining unit 27 for alllight emitter groups. Then, the three-dimensional position and the sizeof the object are obtained. The obtained object information is stored inthe memory 50 together with the detection time. Then, the objectinformation-obtaining process is completed.

Time T3 in FIG. 12 is a calculation time required for obtaining thedistance to the object. In this case, T3 is about 10 μsec. Time T4 inFIG. 12 is a margin time, and it is about 93 μsec. As described above,since the margin time is provided, Time T2 can be freely set dependingon the intended use.

Next, the detection resolution performance of the laser radar 20 will bedescribed. In this case, the size of the area in the object to which thelight is irradiated when the light is irradiated from one light emittergroup to the object is the detection resolution performance. The smallerthe area is, the higher the detection resolution performance is. Thedetection resolution performance relates to a divergence angle of lightemitted from the coupling lens 23 when one light emitter group islighted on. The smaller the divergence angle is, the higher thedetection resolution performance is.

In this case, as illustrated in FIGS. 14A, 14B as one example, thedivergence angle in the Y-axis direction is Ky, and the divergence anglein the Z-axis direction is Kz. In this case, the divergence angle Ky canbe obtained by the following formula (1), and the divergence angle Kzcan be obtained by the following formula (2). In this case, L1 denotes alength of the light emitter group in the Y-axis direction, L2 denotes alength of the light emitter group in the Z-axis direction, and f denotesa focal length of the coupling lens 23.Ky=2×tan−1 (L1/2f)   (1)Kz=2×tan−1 (L2/2f)   (2)

The relationship between the focal length f of the coupling lens 23 andthe divergence angle Ky where L1=313 μm, and the relationship betweenthe focal length f of the coupling lens 23 and the divergence angle Kzwhere L2=159 μm are illustrated in FIG. 15. As illustrated in FIG. 15,the longer the focal length f of the coupling lens is, the smaller thedivergence angle is. Namely, the longer the focal length f of thecoupling lens is, the higher the detection resolution performance is.

Next, the detection region of the laser radar 20 will be described. Inthis case, the detection region is the size of the area in the objectposition to which the light is irradiated when all of the light emittergroups are lighted on (refer to FIGS. 16A, 16B). In addition, since thedetection region differs in accordance with an object position, thedetection region corresponds to the detection angle which is adivergence angle of the light emitted from the coupling lens 23 when allof the light emitter groups are lighted on.

Then, as illustrated in FIGS. 17A, 17B as one example, the detectionangle in the Y-axis direction is θy and the detection angle in theZ-axis direction is θz. In this case, the detection angle θy can beobtained by the following formula (3), and the detection angle θz can beobtained by the following formula (4). In this case, L3 denotes a lengthof the light source 21 in the Y-axis direction, L4 denotes a length ofthe light source 21 in the Z-axis direction, and f denotes a focallength of the coupling lens 23.θy=tan−1 (L3/2f)   (3)θz=tan−1 (L4/2f)   (4)

The relationship between the focal length f of the coupling lens 23 andthe detection angle θy where L3=5.008 mm, and the relationship betweenthe focal length f of the coupling lenxs 23 and the detection angle θzwhere L4=1.908 mm are illustrated in FIG. 18. As illustrated in FIG. 18,the shorter the focal length f of the coupling lens is, the larger thedetection angle is. Namely, the shorter the focal length f of thecoupling lens is, the wider the detection region is.

An appropriate detection region and detection resolution performance canbe set according to the intended use of the laser radar 20.

The focal length of the light-receiving lens 24 is the same as the focallength f of the coupling lens 23. The light receiver 25 includes asingle light-receiving element, and an area (hereinafter referred to asreflected light-receiving area) which receives the light reflected bythe object has the same size as the emission light area of the lightsource 21. Namely, the area has a rectangular shape having 5.008 mm inlength L3 in the Y-axis direction and 1.908 mm in length L4 in theZ-axis direction (refer to FIGS. 19A, 19B).

A light receivable area in a general light-receiving element has acircular shape or a square shape. When such a general light-receivingelement is used as a light-receiving element of the light receiver 25,it is preferable to block the light entering in the region of the lightreceivable area except the reflected light-receiving area because suchlight becomes a noise. In this case, it is preferable to provide a maskincluding an opening so as to block the light entering in the region ofthe light receivable area of the light-receiving element except thereflected light-receiving area. FIG. 20A illustrates a circularlight-receiving element provided with a mask M, and FIG. 20B illustratesa square light-receiving element provided with the mask M. In any case,the light passing through the opening of the mask M is received in thereflected light-receiving area.

In addition, a bandpass filter which transmits only the light reflectedby the object may be provided in the opening of the mask M. For example,when the wavelength of the light emitted from the light source 21 is 905nm, the noise can be further reduced by providing the bandpass filterwhich blocks the light in addition to the light having a wavelength of905±40 nm.

A member having an opening may be provided between the light receiver 25and the light-receiving lens 24 instead of the mask as long as the lighttoward the region in the light receivable area of the light-receivingelement except the reflected light-receiving area is blocked.

Referring to FIG. 2, the main controller 40 determines whether or notthe object is located in front of the vehicle 1 and obtains the size andshape of the object when the object is located in front of the vehicle 1based on the object information stored in the memory 50. The maincontroller 40 also obtains a moving direction, a moving speed, and thelike when the object moves. Such information is then displayed on thedisplay 30.

The main controller 40 outputs alarm information to the sound and alarmgenerator 60 upon the determination of the risk of an accident.

The sound and alarm generator 60 includes a sound synthesizer 61, alarmsignal generator 62, and speaker 63, as illustrated in FIG. 21 as oneexample.

The sound synthesizer 61 includes sound data, selects correspondingsound data upon the reception of the alarm information from the maincontroller 40, and outputs the selected sound data to the speaker 63.

The alarm signal generator 62 generates a corresponding alarm signalupon the reception of the alarm information from the main controller 40,and outputs the alarm signal to the speaker 63.

Meanwhile, in the reflection sensor disclosed in JP 3446466B, the numberof measurement points in an up and down direction is determined based onthe number of surfaces of the polygon mirror. For this reason, thereflection sensor has the small number of measurement points in an upand down direction. When scanning at a wide angle, the laser lightcannot scan in the horizontal direction, and is curved.

In the laser radar disclosed in JP 2894055B, it is difficult to detectan object when a distance to the object is long because the laser lightis diffused, and the energy density is decreased.

As described above, the processor in the object detector of the presentinvention is configured by the object information-obtaining unit 27according to the present embodiment. A monitoring controller in thesensor of the present invention is configured by the main controller 40,the memory 50, and the sound and alarm generator 60.

As described above, the laser radar 20 according to the presentembodiment includes the light source 21, light source driver 22,coupling lens 23, light-receiving lens 24, light receiver 25,light-receiving timing detection unit 26, and objectinformation-obtaining unit 27.

The light source 21 includes a plurality of light emitter groups. Eachlight emitter group includes a plurality of light emitters. With thisconfiguration, each light emitter group ensures the light volumeaccording to the object position of the detection object. As a result, adistance to a detectable object can be increased.

A plurality of light emitter groups is arranged in matrix along theY-axis direction (first direction) and the Z-axis direction (seconddirection). In this case, a desired detection region and detectionresolution performance can be obtained in the Y-axis direction andZ-axis direction by adjusting the focal length of the coupling lens 23.

According to the laser radar 20 of the present embodiment, a distance toa detectable object can be increased, a detection region in an up anddown direction (in this case, Z-axis direction) can be expanded, and adetection resolution performance in an up and down direction can beimproved.

The object information-obtaining unit 27 sequentially lights on andlights off each of a plurality of light emitter groups with the lightsource driver 22, and obtains distance information to the object basedon the lighting-on timing of the light emitter group and thelight-receiving timing of the light-receiver 25 for each of the lightemitter groups. Moreover, the object information-obtaining unit 27obtains the positional information of the object based on the distanceinformation to the object for each of the light emitter groups. In thiscase, the positional information of the object can be accuratelyobtained.

The laser radar 20 according to the present embodiment does not requirea scanning mechanism such as a polygon mirror, so that a trouble lessand reliable laser radar can be provided.

The monitor 10 according to the present embodiment includes the laserradar 20, so that the positional information of the object, the size ofthe object, the shape of the object, the moving direction of the object,the moving speed of the object, and the like can be accurately obtained.

In the above embodiment, the rectangular reflected light-receiving areain the light receiver 25 is described. However, the shape of thereflected light-receiving area can be a square shape by adjusting atleast one of the focal length of the light-receiving lens 24 in theZ-axis direction and the focal length of the light-receiving lens 24 inthe Y-axis direction. In this case, a general light-receiving elementhaving a square light receivable area may be used as the light-receivingelement of the light-receiver 25.

FIG. 22A and FIG. 22B illustrate an example when the focal length of thelight-receiving lens 24 in the Z-axis direction is f1 longer than thefocal length f in the Y-axis direction and the length of the reflectedlight-receiving area in the Z-axis direction is L3.

FIG. 23A and FIG. 23B illustrate an example when the focal length of thelight-receiving lens 24 in the Y-axis direction is 12 shorter than thefocal length f in the Z-axis direction and the length of the reflectedlight-receiving area in the Y-axis direction is L4.

Comparing the example illustrated in FIGS. 22A, 22B to the exampleillustrated in FIGS. 23A, 23B, the example illustrated in FIGS. 23A, 23Buses a light-receiving element smaller than that in the exampleillustrated in FIGS. 22A, 22B because the reflected light-receiving areais small. The costs can be therefore lowered, and the smalllight-receiving element is preferable because it is advantageous for aresponse performance and noise.

In the above embodiment, as illustrated in FIGS. 24, 25 as one example,a coupling lens 23_1 and a coupling lens 23_2 may be used instead of thecoupling lens 23, and a light-receiving lens 24_1 and a light-receivinglens 24_2 may be used instead of the light-receiving lens 24. In thiscase, the example illustrated in FIGS. 24, 25 includes a holder 28 whichholds each lens and an actuator 29 which moves the holder 28 in theZ-axis direction. The actuator 29 is controlled by the light sourcedriver 22.

For example, the coupling lens 23_1 and the light-receiving lens 24_1are a short focus lens (for example, 6 mm), and the coupling lens 23_2and the light-receiving lens 24_2 are a long focus lens (for example, 50nm).

The coupling lens 23_1 and the light-receiving lens 24_1 are used as apair, and the coupling lens 23_2 and the light-receiving lens 24_2 areused as a pair. Each lens is held by the holder 28.

As illustrated in FIG. 24, when the actuator 29 is controlled such thatthe coupling lens 23_1 is located on +X side of the light source 21, andthe light-receiving lens 24_1 is located on +X side of thelight-receiver 25, a wide detection region can be obtained. On the otherhand, as illustrated in FIG. 25, when the actuator 29 is controlled suchthat the coupling lens 23_2 is located on +X side of the light source 21and the light-receiving lens 24_2 is located on +X side of the lightreceiver 25, a high detection resolution performance can be achieved.Namely, the configuration for the wide detection region and theconfiguration for the high detection resolution performance can beswitched.

In this case, the focal length of the coupling lens and the focal lengthof the light-receiving lens which are used simultaneously may differ.

While the focal length of the light-receiving lens may be constant, thefocal length of the coupling lens may be only changed.

A coupling lens system including a zooming function may be used insteadof the coupling lens 23. In this case, the configuration for the widedetection region and the configuration for the high detection resolutionperformance can be switched. For example, the configuration for the widedetection region can be used in an urban location and the configurationfor the high detection resolution performance can be used in a high way.In this case, an urban location or a high way can be determined by asensor provided outside, and the focal length of the coupling lenssystem is changed by a driving mechanism such as an actuator.

When the coupling lens 23 includes vignetting, the volume of the light(refer to FIG. 26A) emitted from the laser radar 20 toward theperipheral part of the detection region may be smaller than the volumeof the light (refer to FIG. 26B) emitted toward the central part of thedetection region. Moreover, when the light-receiving lens 24 includesvignetting, the light-receiving volume when the light incident on thelaser radar 20 is light (refer to FIG. 27A) from the peripheral part ofthe detection region may be smaller than the light-receiving volume whenthe light incident on the laser radar 20 is light from the central partof the detection region. In this case, as illustrated in FIG. 28 as anexample, the timing in which the light-receiving volume exceeds athreshold may differ between the object located in the central part ofthe detection region and the object located in the peripheral part ofthe detection region even though the objects are located in the samedistance. Such a timing difference causes a detection error oflight-receiving timing in the light-receiving timing detection unit 26,resulting in a measurement error of a distance to an object and ameasurement error of an object shape.

When a detection error of the light-receiving time has a negative effecton the detection result, the emission light volume of a plurality oflight emitter groups may be adjusted for each of the light emittergroups such that the light-receiving volume becomes substantially thesame regardless of the position in the detection region as long as thedistance to the object is the same.

For example, the emission light volume of the light emitter groups canbe adjusted such that the ratio between the emission light volume of thelight emitter group for use when the light moves to the peripheral partof the detection region and the emission light volume of the lightemitter group for use when the light moves to the central part of thedetection region becomes 2:1.

In this case, all of the light emitters (in this case, 12560) may belighted on in the light emitter group for use when the light moves tothe peripheral part of the detection region, the half of the lightemitters (in this case, 6280) may be lighted on in the light emittergroup for use when the light moves to the central part of the detectionregion, and the intermediate number of light emitters may be lighted onin the light emitter group between these light emitter groups. Moreover,the driving current of the light emitter group for use when the lightmoves to the peripheral part of the detection region may be set to twicethe driving current of the light emitter group for use when the lightmoves to the central part of the detection region, and the drivingcurrent of the light emitter group between these light emitter groupsmay be intermediate driving current between these driving current.

In this case, even though the distance to the object is short, thesaturation of the light receiver 25 due to the excessive light-receivingvolume can be controlled, so that a time until next detection can beshortened.

The volume of the reflected light from the object is inverselyproportional to the square of the distance to the object. For example,the volume of the reflected light when the distance to the object is 40m is four times the light volume of the reflected light when thedistance to the object is 80 m. Such a difference in light volume causesa detection error of the light-receiving timing similar to the above. Asa result, the measurement error of the distance to the object and themeasurement error of the object shape may be caused.

When a detection error of the light-receiving timing has a negativeeffect on the detection result, the emission light volume of the lightemitter groups may be adjusted such that the light-receiving volumebecomes the same regardless of the distance to the object.

For example, preliminary detection is most recently performed, then, thedistance to the object is generally estimated from the detection result,and the emission light volume of the light emitter groups is adjustedbased on the estimated result.

In this case, for example, when the estimated distance to the object is200 m, all of the light emitters (in this case, 12560) may be lightedon. When the estimated distance to the object is 100 m, ¼ times thelight emitters (in this case, 3140) may be lighted on. The drivingcurrent when the estimated distance to the object is about 100 m may be¼ times the driving current when the estimated distance to the object is200 m.

In this case, even though the distance to the object is short, thesaturation of the light receiver 25 due to the excessive light volumecan be controlled, and a time until next detection can be shortened.

In the above embodiment, an assembly including two or more light emittergroups may be an assembly light emitter group F (k, m). For example, oneassembly light emitter group including adjacent 16 light emitter groupsis illustrated in FIG. 29. In this case, F (1, 1) includes G (1, 1), G(1, 2), G (1, 3), G (1, 4), G (2, 1), G (2, 2), G (2, 3), G (2, 4), G(3, 1), G (3, 2), G (3, 3), G (3, 4), G (4, 1), G (4, 2), G (4, 3), andG (4, 4). F (3, 1) includes G (9, 1), G (9, 2), G (9, 3), G (9, 4), G(10, 1), G (10, 2), G (10, 3), G (10, 4), G (11, 1), G (11, 2), G (11,3), G (11, 4), G (12, 1), G (12, 2), G (12, 3), and G (12, 4).

In this case, in the object information-obtaining process, asillustrated in FIG. 30, each of the assembly light emitter groups islighted on until the existence of the object is determined. After thedetermination of the existence of the object, each of the light emittergroups may be lighted on in next detection timing. The process timewithout an object can be therefore shortened.

Upon the switching on of the power source, the flag f showing theexistence or non-existence of the object is set to an initial value 0 inthe first Step S501.

In the next Step S503, it is determined whether or not the value of theflag f is 0. When the value of the flag f is 0 (YES in S503), theprocess moves to Step S505.

In Step S505, each of the assembly light emitter groups is lighted on,and the existence or non-existence information of the object isobtained.

In the next Step 5507, the existence of the object is determined. Whenthe existence of the object is determined (YES in S507), the processmoves to Step S509. On the other hand, when there is no object (NO inS507), the process returns to Step S503.

In Step S509, the flag f is set to 1. Then, the process returns to StepS503.

In step 5503, when the value of the flag f is not 0 (NO in S503), theprocess moves to step S511.

In Step S511, as illustrated in FIG. 11, each of light emitter groups islighted on, and the object information is obtained.

In the next Step S513, the existence of the object is determined. Whenthe existence of the object is determined (YES in S513), the processreturns to Step S503. On the other hand, when there is no object (NO inS513), the process moves to Step S515.

In Step S515, the flag f is set to 0. Then, the process returns to StepS503.

FIG. 31 illustrates the details of the process in Step S505.

In the first Step S601, the valuable numbers k, m, which specify theassembly light emitter group, are set to the initial value 1.

In the next Step S603, the assembly light emitter group F (k, m) isselected.

In the next Step S605, the lighting of the selected assembly lightemitter group F (k, m) is instructed to the light source driver 22. Thelight source driver 22 thereby simultaneously lights on all of the lightemitters in the assembly light emitter group F (k, m) for apredetermined time T1 (refer to FIG. 12).

In the next Step S607, the timer counter TC is reset to 0.

In the next Step S609, it is determined whether or not the lightreflected by the object is received by the light receiver 25 based onthe light-receiving timing signal from the light-receiving timingdetection unit 26. When the light receiver 25 does not receive the light(NO in S609), the process moves to Step S611.

In Step S611, it is determined whether or not the value of the timercounter TC is equal to a value corresponding to T1+T2 (refer to FIG. 12)or more. In this case, T2 is 1.3 μsec, as one example. When there is nointerruption at the time that the value of the timer counter TC reachesa value corresponding to T1+T2 from the interruption controller (NO inS611), the process returns to Step S609.

In Step S609, when the light receiver 25 receives light (YES in S609),the process moves to Step S613.

In Step S613, the existence of the object is determined. Then, theobject existence information is stored in a not-shown memory of theobject information-obtaining unit 27, and the process moves to StepS619.

In Step S611, when there is the interruption at the time that the valueof the timer counter TC reaches a value corresponding to T1+T2 from theinterruption controller (YES in S611), the process moves to Step S617.

In the next Step S617, the non-existence of the object is determined.The non-existence object information is stored in a not-shown memory ofthe object information-obtaining unit 27.

In Step S619, it is determined whether or not the value of the timercounter TC is equal to a value corresponding to the time T0 (refer toFIG. 12) or not. When there is no interruption at the time that thevalue of the timer counter TC reaches a value corresponding to T0 fromthe interruption controller (NO in S619), the process waits for theinterruption. When there is the interruption (YES in S619), the processmoves to Step S621.

In Step S621, it is determined whether or not the value of the valuablenumber m is equal to 4 or more. When the value of the valuable number mis less than 4 (NO in S621), the process moves to Step S623.

In Step S623, 1 is added to the value of the valuable number m, and theprocess returns to Step S603.

After that, the processes in Steps S603 to S623 are repeated until it isdetermined that the value of the valuable number m reaches equal to 4 ormore.

When the value of the valuable number m is equal to 4 or more (YES inS621), the process moves to Step S625.

In Step S625, it is determined whether or not the value of the variablenumber k is equal to 3 or more. When the value of the variable number kis less than 3 (No in S625), the process moves to Step S627.

In Step S627, 1 is added to the value of the variable number k.

In the next Step S629, the value of the variable number m is returned tothe initial value 1, and the process returns to Step S603.

After that, the processes in Steps S603 to S629 are repeated until it isdetermined that the value of the variable number k reaches equal to 3 ormore.

When the value of the variable number k is equal to 3 or more, theprocess in Step S505 is completed.

When the light emitter group is lighted on, a temperature of theperipheral part of the light emitter group is increased. When theadjacent light emitter groups are sequentially lighted on, the emissionlight volume may be decreased even though the driving current is thesame.

When a decrease in emission light volume has a negative effect on thedetection result, the light emitter group at least one light emittergroup away from the previously lighted-on light emitter group may belighted on.

In this case, the even-numbered light emitter groups G (1, 2), G (1, 4),G (1, 6) . . . G (1, 16) may be lighted on after the odd-numbered lightemitter groups G (1, 1), G (1, 3), G (1, 5) . . . G (1, 15) are lightedon. In addition, the lighting order includes various orders.

A rotation mechanism which rotates the laser radar 20 about Z-axis maybe provided in the above embodiment.

In the above embodiment, 157 light emitters are arranged along theY-axis direction, and 80 light emitters are arranged along the Z-axisdirection in each light emitter group G. However, the present inventionis not limited the above embodiment.

In the above embodiment, each light emitter group G includes 12560 lightemitters. However, the present invention is not limited the aboveembodiment.

In the above embodiment, the light output of one light emitter is 2 mW.However, the present invention is not limited the above embodiment.

In the above embodiment, the light output of one light emitter group Gis about 25 W. However, the present invention is not limited to theabove embodiment.

In the above embodiment, the diameter ds of one emitter is 1 μm, thedistance D1 between two light emitters adjacent to each other in theY-axis direction is 1 μm, and the distance D2 between two light emittersadjacent to each other in the Z-axis direction is 1 μm. However, thepresent invention is not limited the above embodiment.

In the above embodiment, the length L1 of one light emitter group G inthe Y-axis direction is 313 μm, and the length L2 of one light emittergroup G in the Z-axis direction is 159 μm. However, the presentinvention is not limited the above embodiment.

In the above embodiment, 16 light emitter groups G are arranged alongthe Y-axis direction and 12 light emitter groups G are arranged alongthe Z-axis direction in the light source 21. However, the presentinvention is not limited the above embodiment.

In the above embodiment, the light source 21 includes 192 light emittergroups G. However, the present invention is not limited the aboveembodiment.

In the above embodiment, T1=0.02 μsec. However, the present invention isnot limited the above embodiment.

In the above embodiment, T0=104 μsec. However, the present invention isnot limited the above embodiment.

In the above embodiment, the object information-obtaining process isrepeated once in 20 msec. However, the present invention is not limitedthe above embodiment. For example, the execution interval of the objectinformation-obtaining process may differ according to a moving speed ofa vehicle.

In the above embodiment, the main controller 40 may execute a part ofthe process in the object information-obtaining unit 27, and the objectinformation-obtaining unit 27 may execute a part of the process in themain controller 40.

In the above embodiment, the monitor 10 includes one laser radar 20.However, the present invention is not limited the above embodiment. Themonitor 10 may include a plurality of laser radars 20 according to thesize of a vehicle, a monitoring area, and the like.

In the above embodiment, the laser radar 20 is used for the monitor 10which monitors the traveling direction (forward) of the vehicle.However, the present invention is not limited the above embodiment. Thelaser radar 20 may be used for a device which monitors a back or a sideof a vehicle.

The laser radar 20 can be used for a sensor in addition to a sensormounted on a vehicle. In this case, the main controller 40 outputs alarminformation according to a purpose of sensing.

The laser radar 20 can be used for a different purpose (for example,measurement device) other than a sensor.

According to the object detector of the present embodiment, a distanceto a detectable object can be increased, a detection region in an up anddirection can be expanded, and a detection resolution performance in anup and down direction can be improved.

In addition, although the embodiment of the present invention has beendescribed above, the present invention is not limited thereto. It shouldbe appreciated that variations may be made in the embodiment describedby persons skilled in the art without departing from the scope of thepresent invention.

What is claimed is:
 1. An object detector, comprising: a projectorincluding a light source having a two-dimensionally arranged pluralityof light emitter groups, each of the light emitter groups having aplurality of light emitters and configured to emit an adjustableemission light volume; a light receiver which receives light emittedfrom the projector and reflected by an object; a light source driverwhich illuminates and turns off each of the light emitter groups of thelight source; and a processor which sequentially illuminates and turnsoff the plurality of light emitter groups using the light source driver,and obtains distance information to the object based on lighting-ontiming of one of the light emitter groups which has emitted light andlight-receiving timing of the light receiver when the light receiverreceives light reflected by the object, the processor being configuredto adjust the emission light volume based on the distance information tothe object.
 2. The object detector according to claim 1, wherein theprocessor sequentially causes the light source driver to illuminate oneof the light emitter groups which is at least one light emitter groupaway from a previously illuminated light emitter group.
 3. The objectdetector according to claim 1, wherein: the projector includes aprojection optical system disposed on an optical path of light emittedfrom the light source, and a focal length of the projection opticalsystem is variable.
 4. The object detector according to claim 1,wherein: the light receiver includes a single light-receiving elementhaving a light receiving area, and a size of the light-receiving area ofthe light receiver is a same size as a size of an emission area of theplurality of light emitter groups when the plurality of light emittergroups in the light source are simultaneously illuminated.
 5. The objectdetector according to claim 1, wherein: the plurality of light emittergroups is disposed along a first direction and a second directionorthogonal to each other, the light receiver includes a light-receivingoptical system which collects the light reflected by the object, and thelight-receiving optical system has a focal length which differs betweenthe first direction and the second direction.
 6. The object detectoraccording to claim 1, wherein the light emitter groups disposed in aperipheral part of the plurality of light emitter groups have anemission light volume larger than that of the light emitter groupsdisposed in a central part of the plurality of light emitter groups. 7.An object detector, comprising: a projector including a light sourcehaving a two-dimensionally arranged plurality of light emitter groups,each of the light emitter groups having a plurality of light emitters; alight receiver which receives light emitted from the projector, andreflected by an object; a light source driver which illuminates andturns off each of the light emitter groups of the light source; and aprocessor which sequentially illuminates and turns off the plurality oflight emitter groups using the light source driver, and obtains distanceinformation to the object based on lighting-on timing of the lightemitter group and light-receiving timing of the light receiver when thelight receiver receives light reflected by the object, the processorbeing configured to adjust a number of light emitters to be illuminatedin one of the light emitter groups based on the distance information tothe object.
 8. The object detector according to claim 7, wherein theprocessor sequentially illuminates the light emitter group at least onelight emitter group away from a previously illuminated light emittergroup.
 9. The object detector according to claim 7, wherein: theprojector includes a projection optical system disposed on an opticalpath of light emitted from the light source, and a focal length of theprojection optical system is variable.
 10. The object detector accordingto claim 7, wherein: the light receiver includes a singlelight-receiving element having a light receiving area, and a size of thelight-receiving area is a same size as a size of an emission area of theplurality of light emitter groups when the plurality of light emittergroups in the light source are simultaneously illuminated.
 11. Theobject detector according to claim 7, wherein: the plurality of lightemitter groups is disposed along a first direction and a seconddirection orthogonal to each other, the light receiver includes alight-receiving optical system which collects the light reflected by theobject, and the light-receiving optical system has a focal length whichdiffers between the first direction and the second direction.
 12. Theobject detector according to claim 7, wherein the light emitter groupsdisposed in a peripheral part of the plurality of light emitter groupshave an emission light volume larger than that of the light emittergroups disposed in a central part of the plurality of light emittergroups.
 13. The object detector according to claim 7, wherein theprocessor sequentially causes the light source driver to illuminate oneof the light emitter groups which is at least one light emitter groupaway from a previously illuminated light emitter group.
 14. The objectdetector according to claim 7, wherein: the projector includes aprojection optical system disposed on an optical path of light emittedfrom the light source, and a focal length of the projection opticalsystem is variable.
 15. The object detector according to claim 7,wherein: the light receiver includes a single light-receiving elementhaving a light receiving area, and a size of the light-receiving area ofthe light receiver is a same size as a size of an emission area of theplurality of light emitter groups when the plurality of light emittergroups in the light source are simultaneously illuminated.
 16. Theobject detector according to claim 7, wherein: the plurality of lightemitter groups is disposed along a first direction and a seconddirection orthogonal to each other, the light receiver includes alight-receiving optical system which collects the light reflected by theobject, and the light-receiving optical system has a focal length whichdiffers between the first direction and the second direction.
 17. Theobject detector according to claim 7, wherein the light emitter groupsdisposed in a peripheral part of the plurality of light emitter groupshave an emission light volume larger than that of the light emittergroups.
 18. An object detector, comprising: a projector including alight source having a two-dimensionally arranged plurality of lightemitter groups, each of the light emitter groups having a plurality oflight emitters; a light receiver which receives light emitted from theprojector, and reflected by an object; a light source driver whichilluminates and turns off each of the light emitter groups of the lightsource; and a processor which sequentially illuminates and turns off theplurality of light emitter groups with the light source driver, andobtains distance information to the object based on lighting-on timingof one of the light emitter groups which has emitted light andlight-receiving timing of the light receiver when the light receiverreceives light reflected by the object, the processor being configuredto adjust the emission light volume based on the distance information tothe object.